I always go for Verbatim as i have never had any problems with them, but they won't be the cheapest. You may be able to pick up 50 for £10 though at a guess.
This is what i have bought in the past for movies etc, 100 for £17.
http://www.amazon.co.uk/dp/B000BEZYL...SIN=B000BEZYLA
Edit
These are DVD-R though not that that should be an issue and i don't know what is best but i have never used DVD+R.